(a) Field of the Invention
The present invention relates to a production control system for manufacturing various types of electron devices through various stages in which a plurality of apparatuses of the same kind operate for processing the devices.
(b) Description of the Related Art
In conventional production control systems for manufacturing electron devices of various types, productive instruction data are determined based on a state of a production line predicted by a simulator, or else productive instruction data are determined by an expert system in which know-how of experts for efficiently operating the production line is stored as a knowledge base. These systems are intended to solve a problem of how to convert collected status data off the production line into productive instruction data. These systems are introduced because such a conversion cannot be attained by a simple algorithm in the case of production of electron devices which involves a large number of and many kinds of stages, many kinds of orders of stages, and many kinds of manners of processing in the equipment through which lots of devices pass.
FIG. 1 is a block diagram showing a conventional production control system for manufacturing electron devices. An example of such a production control system is disclosed in Japanese Patent Laid-open Publication No. 2-224954. As shown in FIG. 1, the production control system comprises data collecting means 12 for collecting status data, such as current operating conditions and progress of production, from a production line 11 including a variety of apparatuses assigned for a plurality of stages including stage 1 through stage n, productive instruction data inputting means 31 for inputting productive instruction data such as designation of type and quantity of product to be manufactured, and a central processing unit 32 which has an expert system 33 including a knowledge base 35 containing accumulated know-how of experts and a simulator 34 for predicting operating conditions at an arbitrary future point of time and which receives external data from the productive instruction data inputting means 31 and from the data collecting means 12 to create and transmit a new productive instruction data for the production line 11 via communicating means 13.
The expert system 33 creates appropriate productive instruction data from data, which are obtained from the data collecting means 12 and from the productive instruction data inputting means 31, on the basis of know-how of experts accumulated in the knowledge base 35. During this data creating process by the expert system 33, if a judging rule in the knowledge base 35 requires data on a future state of production on the production line 11, the expert system 33 directs the simulator 34 to predict a future state on the production line 11, then creates productive instruction data based on the results of the prediction. The simulator 32 calculates prediction data based on data obtained from the data collecting means 12 and reports the prediction data to the expert system 33. The expert system 33 then transfers productive instruction data thus obtained to the production line including apparatuses of stage 1 through stage n via the communicating means 13.
In the conventional production control system as described above, the expert system 33 is generally assigned to allocate lots to the individual apparatuses, and the simulator 34 is assigned to predict a state of the production line when required, whereby an optimum productive instruction data is obtained for carrying out efficient production. The conventional production control system, however, involves various problems when applied to a complex production line as for semiconductor devices.
One of those problems is that productive instruction data cannot be created promptly because it takes a lot of time for a simulator to carry out simulation. This is because a simulation is quite complex due to the facts that a process for the production of one semiconductor device involves hundreds of stages, from tens to hundreds of patterns regarding the order of stages in the process and nearly a hundred kinds of apparatuses involved in the process and that a single process employs the same apparatus repeatedly with or without looping. For example, simulation for a single process takes one hour or more, although the amount of time required for simulation varies more or less depending on production lines. This raises a problem of a delay in start-up of a production line and a reduction in availability factor of the apparatuses.
Another problem is that, although incorporating of know-how of experts into a system is applicable to stages of up to certain complexity, it cannot provide the optimum productive instruction data to the production line for semiconductor device in which many types of products are produced in the same production line and in which the production stages are diversified and complex. This is partly because know-how varies depending on types of products or stages, partly because it is therefore impossible to obtain know-how which is common among the stages, and partly because it is not obvious whether know-how itself is most suited to the process.